If you're using Lion or Mountain Lion, Outlook 2011 isn't able to import e-mail from the Mail client. There are third party apps available to do this (or you can do it manually), but.... Microsoft has advised they have no intention of fixing this problem.

Also, Outlook doesn't offer the ability to resize an image/video like you can with Mail.

I used it for about two weeks and got totally frustrated with its shortcomings. Went back to Mail. I only use Word and Excel if I absolutely have to.

I recently moved away from outlook to the native mail, contact and calendar apps using a hosted exchange account. I liked outlook good enough since I use it a lot on my PCs at home and at work but I ran into some nasty glitches where I was getting numerous duplicate calendar entries being created only on the mac outlook. the PC outlook and OWA work as expected but as any event came up in my calendar, such as a birthday, outlook on the mac would always create at least one duplicate entry of the event. I've even seen outlook on the mac continuously create duplicate events as I was trying to delete the first duplicates, drove me crazy!! never had any problems with mail or contacts but the calendar was absolutely unacceptable.

I use it on one of my iMacs at home and have had no problems with it. It works well and does what I need it to do occasionally. My wife actually uses it more than I do, hence why I run it on one of my iMacs. She is a legal secretary and is quite use to all of its features as that is what she uses at work. She thoroughly enjoys using it and has no problems either. And she uses it hard. Lot different than Entourage.

I think it works reasonably well. If you client is a previous Outlook user they will be pretty much right at home. A big step up from Entourage in most respects, a few steps back (such as the unified dashboard etc.)

I use it daily on my business Mac although i do find myself going back and fourth between mail.app

If your client is going to use the calendar heavily, be ware of some issue such as the duplicating issue they have had but overall its a Windows like Outlook experience.